The invention relates to the process measurement and control industry. The measurement and control industry employs process variable transmitters to remotely monitor process variables associated with fluids such as slurries, liquids, vapors, gasses, chemicals, pulp, petroleum, pharmaceuticals, food and other food processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties.
FIG. 1 is an exploded view of a prior art process flow device 50 for measuring process variables, such as differential pressure and flow. As shown in FIG. 1, flow plate 52 is clamped between flanges 54, 56 in a flow path to produce a differential pressure across a constriction for measuring flow rate of fluids through a pipe 58. Differential pressure across the flow constriction is measured at pressure taps 60, 62. As illustrated in FIGS. 1-2, pressure taps 60, 62 are separate from flow plate 52 clamped between pipe flanges 54, 56 so that seams separate pressure taps 60, 62 from flow plate 52. Pipe 58 conveys process fluid at a high pressure. Such pressure is a combination of the differential pressure developed in response to the constriction and the static pressure within the pipe which can be 1000 psi or more. The high pressure can cause fluid and pressure to leak from seams between the flow plate 52 and pressure taps 60, 62. Vibration and other motion of the flow pipe can loosen the connection between the flow plate 52 and pressure taps 60, 62 contributing to fluid and pressure leakage at the seams.
Within device 50, flow rate is calculated based upon differential pressure across a flow constriction, pipe diameter and constriction profile. Pressure loss and leakage at seams changes the measured differential pressure across the flow constriction and the pressure loss or change is not attributable to flow rate. The non-attributable pressure loss at the seams degrades flow calculations. Additionally, device 50 requires significant field installation time due to the necessity of joining all the couplings together and performing leak checking upon the couplings. Moreover, whenever maintenance is required for device 50, significant disassembly/reassembly time is usually required which increases undesirable downtime. Thus, it is desirable to provide a process fluid flow measurement device with increased accuracy and reduced field installation time, downtime, and cost.